Getting a PMP then

If you have already learned a lot from other PMs, you should make your desire of becoming one known. Discuss with your boss during performance reviews. Find the right opportunity to step up and advertise yourself. For example, that Chinese client project would have been a good case for you to talk to the key people about potentially for you to play the PM role or part of it. I think most consulting firms like their people to have very clear idea about their career direction and being aggressive about pursuing it.

Most PMs are PMP certified but I can tell you that most of them didn't start that way because the PMP requires PM experience to start with. So it gets back to YOU are the most important factor. If that's what you want to do, you are in the perfect place to learn, and to push for opportunities to demonstrate yourself. The first time you bring up your desire, your boss would probably discount it or give you the runaround. What you do? Ask for advise on how to get there. Try to learn/improve on the things and try again with your boss a couple of months down the road.

You have to demonstrate your capability and earn it. I know many consulting firms don't believe business experience alone is nearly as enough to do PM. For example, most of the PMs at Avanade are former developers, network engineers etc.

Again focus on gaining the real skills and experiences and be aggressive about going in the direction you desire. It's a fiction that an MBA degree would give you instant credibility.